1. Field
The present disclosure generally relates to multi-chip modules (MCMs) and techniques for fabricating MCMs. More specifically, the present disclosure relates to an MCM that includes substrates that are bonded to each other using an adhesive.
2. Related Art
Multi-chip modules (MCMs) are being developed to facilitate proximity communication (such as capacitively coupled communication) between multiple integrated circuits (ICs) for the next generation of high-performance computers. In these MCMs, adjacent chips are often positioned face-to-face so that information can be communicated between proximity connectors (such as metal pads) on surfaces of facing chips. To facilitate ultrafast chip-to-chip communications via capacitive coupling between the proximity connectors, these chips need to be accurately positioned so that the proximity connectors are horizontally aligned on a micrometer scale, with a gap or spacing of a few microns or less between the proximity connectors on the facing chips.
A simple and elegant technique for assembling the chips in an MCM involves the use of an adhesive to bond the chips together to maintain the desired horizontal and vertical alignment between the proximity connectors. However, there is a tradeoff between the strength of the adhesive layer between a pair of chips and the signal quality during proximity communication. In particular, if the adhesive layer or bondline is thick (e.g., a thickness of 10 μm or more), the adhesive layer is ductile, but this increases the spacing between the proximity connectors, which significantly decreases the signal coupling and the signal quality. Alternatively, if a thin adhesive layer is used, the signal coupling and signal quality are improved, but the adhesive layer is susceptible to shearing failure under lateral stress and strain, which decreases the reliability of the MCM.
Hence, what is needed are an MCM and an associated fabrication technique that do not suffer from the above-described problems.